1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices, and more particularly, to a method of eliminating an oxide layer such as a natural oxide layer, and a semiconductor manufacturing apparatus for use in the removal of the oxide layer.
2. Description of the Related Art
Silicon wafers are susceptible to react with oxygen or moisture in the air, and thus a silicon dioxide (SiO2) layer, which deteriorates the characteristics of a semiconductor device, is formed on the surface of a silicon wafer by spontaneous oxidation. For example, if such a natural oxide layer is formed on the surface of contacts, contact resistance increases. Also, if a natural oxide layer is formed before growth of a gate oxide layer, the characteristics of the gate oxide layer can be altered or deteriorated.
The most popular method used to remove a natural oxide layer in semiconductor fabrication is a wet cleaning technique. In the wet cleaning technique, a hydrofluoric acid (HF), which has a high selectivity between the silicon dioxide to be removed and the silicon wafer, is used as an etching solution. Also, the hydrofluoric acid has an additional advantage of coating the surface of the silicon wafer with hydrogen, in addition to the intrinsic function of removing the silicon dioxide.
However, in the case of using the HF acid to eliminate an oxide layer, other manufacturing steps cannot be carried out in-situ and thus contamination more likely occurs after the cleaning process, increasing the period of time required to complete the overall manufacturing process.
Another disadvantage is that cleaning step with the HF acid must be accompanied by a drying process. However, it is not possible to control the contamination that may occur during the drying process.
In addition, when a semiconductor wafer to be cleaned has small, deep contact holes, inevitably the cleaning solution enters the contact holes. However, due to the intrinsic viscosity of the cleaning solution, the rinsing solution may remain in the small, deep contact holes. Thus, removal of the residues remaining after the cleaning process is also an important concern.
Alternatively, the natural oxide layer can be removed by a dry etching process. For dry etching, a reactive ion etching technique is used with a gas mixture containing tetra-fluoro methane (CF4) and hydrogen (H2), or tri-fluoro methane (CHF3) and oxygen (O2). However, the dry etching process also leaves fluorine (F) on the surface of a silicon wafer which is the underlying layer of the oxide layer. Furthermore, the amount of fluorine remaining after the dry etching process is greater compared to using the wet cleaning technique, and thus the produced semiconductor device may be deteriorated to a greater degree by the dry etching process.
Also, during the dry etching process, damage to the surface of the silicon wafer occurs by the implantation energy of the etching gas, so that the surface of the silicon wafer becomes rough, and a pn junction underneath the wafer surface may be damaged.